DNA Extraction

The first step in DNA analysis is surprisingly simple. That is to isolate the DNA and remove the rest of the cellular material from the sample. To accomplish this, the sample is mixed with a detergent causing cell membranes to burst open and release their DNA along with other cell contents. This is called cell lysis. The mixture is washed with a buffer (mild salt solution) to dilute cellular debris. The samples are then centrifuged causing the cell debris to be pulled from the liquid to form a pellet in the bottom of the centrifuge tube. The DNA remains in solution in the buffer.

The solution then may be treated with enzymes that denature or break down remaining proteins. Sometimes the enzyme RNAse is added to break up any remaining RNA. The mixture is then treated with a salt solution to make the digested proteins and RNA clump together. The mixture is centrifuged again to remove those solids.

Finally the DNA is separated from the chemicals used in the extraction process. One common method for that is to add cold ethanol to the solution. DNA is not soluble in alcohols and will form clumps. Another ride in the centrifuge will cause the now insoluble DNA to form a pellet in the bottom of the tube. The supernatant (liquid) can then be removed and the DNA stored by refrigerating in a buffer solution until needed.

Alternatively, the DNA solution can be run through a column of beads that have been treated so that they bind to the DNA while the rest of the solution flows out of the tube and is discarded. After the beads are washed thoroughly, they are treated with a salt solution that causes the DNA to be released.

The DNA you extract in your kitchen is still contaminated with cellular and other debris from your mouth. A DNA extraction that yields DNA pure enough for sequencing base pairs and comparing with DNA from other sources requires more sophisticated resources than your kitchen. This is especially true when performing DNA analysis for medical or forensic purposes. The video below demonstrates how DNA is isolated and purified in professional lab settings. The Genetic Science Learning Center has a Biotechnics Virtual Lab where you can do your own simulation of a professional laboratory DNA extraction.

In labs where massive numbers of samples are processed daily, elaborate, high tech robotic arms process multiple samples at once. This last video for this topic is a commercially made promotional video for a Thermo Fisher Scientific Instrument designed to process multiple samples quickly and efficiently with maximum precision. This is just one example of a myriad of instruments that are available to commercial labs. New versions and technologies are arriving nonstop. Used models are available on eBay as labs continuously upgrade their instrumentation.